When an AUV or a UUV leaves on mission, it performs its mission at depth and returns to the surface in order to be retrieved by a surface vessel. Now, the AUV or the UUV does not always surface at the position at which it should theoretically surface. Operators located on the surface of the water, or on land, need to know the position of the AUV or UUV to come to retrieve it. The AUV or UUV may, moreover, need to know its position at a given moment in its mission. It then surfaces before diving again. This is called self-relocation. Then, during a mission, in the context of a “pack of AUV or UUV”, the latter may be required to exchange data between them or with another platform, and thus surface for that purpose.
The AUVs or UUVs are therefore conventionally equipped with a wireless antenna for receiving satellite signals in a line of sight with satellites and an emitting wireless antenna making it possible to transmit the position of the vehicle remotely or exchange data with the outside world. These antennas have to be extended as far as possible above the surface of the water to allow for the reception of the signals emitted by the satellites and the transmission of wireless signals with good performance levels.
The antennas are generally installed on a fixed strut extending vertically above the underwater vehicle. This arrangement offers the advantage of being insensitive to the sea conditions, compared to a so-called flush arrangement in which the antennas are flush with the surface of the body of the AUV or of the UUV. The flush antennas are covered with a thin layer of salt water, which covers the antennas, which degrades the performance of the antenna in heavy sea conditions. The flush antennas stop being efficient beyond a sea condition 2. The arrangement on a fixed strut does, however, present the drawback of affecting the hydrodynamic profile of the vehicle and its navigation.
One solution for mitigating these drawbacks is to install the antennas on a deployable strut which is retracted, that is to say drawn back into the body of the vehicle when it is navigating and which is extended out of the body for communication when the vehicle resurfaces. These are called deployable antennas. There are different types of deployable antennas. In a first type, the antennas are deployed by the translation of the strut in a radial direction defined relative to the longitudinal axis of the AUV. This is called hoistable strut. The strut in retracted position then extends along a diameter of the vehicle. This first solution considerably affects the accommodation capacity in the AUV, which significantly reduces its payload. In a second solution, the strut is deployed by rotation about a horizontal axis at right angles to the longitudinal axis of the underwater vehicle. In its retracted position, the strut extends parallel to the longitudinal axis of the AUV and, in its deployed position, along a vertical axis. The drawback of this solution is that it affects the rake of the AUV. The further the communication equipment has to be extended above the surface of the water, the longer the strut has to be and the more the length of the AUV has to be increased accordingly. In other words, the performance s of the antennas are highly dependent on a length of a portion of the underwater vehicle, which is utilized and a length which the strut can extend.
The aim of the invention is to mitigate all or some of these abovementioned drawbacks.